Method for production of styrene from toluene and methane

ABSTRACT

A process is disclosed for making styrene by converting methanol to formaldehyde in a reactor then reacting the formaldehyde with toluene to form styrene in a separate reactor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.14/093,667, filed on Dec. 2, 2013, which is a Continuation of U.S.application Ser. No. 12/345,550, filed on Dec. 29, 2008, now issued asU.S. Pat. No. 8,686,205.

FIELD

The present invention relates to a method for the production of styrene.

BACKGROUND

Styrene is an important monomer used in the manufacture of manyplastics. Styrene is commonly produced by making ethylbenzene, which isthen dehydrogenated to produce styrene. Ethylbenzene is typically formedby one or more aromatic conversion processes involving the alkylation ofbenzene.

Aromatic conversion processes, which are typically carried out utilizinga molecular sieve type catalyst, are well known in the chemicalprocessing industry. Such aromatic conversion processes include thealkylation of aromatic compounds such as benzene with ethylene toproduce alkyl aromatics such as ethylbenzene. Typically an alkylationreactor, which can produce a mixture of monoalkyl and polyalkylbenzenes, will be coupled with a transalkylation reactor for theconversion of polyalkyl benzenes to monoalkyl benzenes. Thetransalkylation process is operated under conditions to causedisproportionation of the polyalkylated aromatic fraction, which canproduce a product having an enhanced ethylbenzene content and reducedpolyalkylated content. When both alkylation and transalkylationprocesses are used, two separate reactors, each with its own catalyst,can be employed for each of the processes.

Ethylene is obtained predominantly from the thermal cracking ofhydrocarbons, such as ethane, propane, butane, or naphtha. Ethylene canalso be produced and recovered from various refinery processes. Thermalcracking and separation technologies for the production of relativelypure ethylene can account for a significant portion of the totalethylbenzene production costs.

Benzene can be obtained from the hydrodealkylation of toluene thatinvolves heating a mixture of toluene with excess hydrogen to elevatedtemperatures (for example 500° C. to 600° C.) in the presence of acatalyst. Under these conditions, toluene can undergo dealkylationaccording to the chemical equation: C₆H₅CH₃+H₂→C₆H₆+CH₄. This reactionrequires energy input and as can be seen from the above equation,produces methane as a byproduct, which is typically separated and mayused as heating fuel for the process.

In view of the above, it would be desirable to have a process ofproducing styrene that does not rely on thermal crackers and expensiveseparation technologies as a source of ethylene. It would further bedesirable to avoid the process of converting toluene to benzene with itsinherent expense and loss of a carbon atom to form methane. It would bedesirable to produce styrene without the use of benzene and ethylene asfeedstreams.

SUMMARY

An embodiment of the present invention is a process for making styreneby converting methanol to formaldehyde in one or more first reactors toform a first product stream comprising formaldehyde and reacting theformaldehyde with toluene in one or more second reactors to form asecond product stream comprising styrene. The first product stream caninclude one or more of hydrogen, water, or methanol. The methanol, ifany is present, can be separated from the first product stream andrecycled to the one or more first reactors.

The process can include utilizing one or more oxidation reactors toconvert methanol into formaldehyde and water to form the first productstream. The process can optionally include utilizing one or moredehydrogenation reactors to convert methanol into formaldehyde andhydrogen to form the first product stream.

The second product stream can include one or more of toluene, water, orformaldehyde. The toluene and/or formaldehyde, if any is present, can beseparated from the second product stream and recycled to the one or moresecond reactors. The one or more second reactors can include a reactionzone under reaction conditions containing a catalyst for reactingtoluene and formaldehyde to form styrene. The process can includepassing the first product stream to a separation stage for separatingformaldehyde from the first product stream. The separation stage cancomprise a membrane separation capable of removing hydrogen from theformaldehyde stream.

Another embodiment of the present invention is a process for makingstyrene by converting methanol to formaldehyde in one or more firstreactors to form a first product stream comprising one or more offormaldehyde, hydrogen, water, or methanol. The first product streamproceeds to a first separation stage for separating formaldehyde fromthe first product stream. The separation stage can include a membraneseparation unit capable of removing hydrogen from the formaldehydestream prior to the secdon reactor.

Toluene and formaldehyde are reacted in one or more second reactors toform a second product stream comprising one or more of styrene, toluene,water, or formaldehyde. The second product stream then passes to asecond separation stage for separating styrene from the second productstream. Methanol, of present, can be separated from the first productstream and recycled to the one or more first reactors. Toluene andformaldehyde, if present, can be separated from the second productstream and recycled to the one or more second reactors.

The process can include utilizing one or more oxidation reactors toconvert methanol into formaldehyde and water to form the first productstream. The process can optionally include utilizing one or moredehydrogenation reactors to convert methanol into formaldehyde andhydrogen to form the first product stream. The one or more secondreactors can comprise a reaction zone under reaction conditionscontaining a catalyst for reacting toluene and formaldehyde to formstyrene. The catalyst can be a basic or neutral catalyst, and can be abasic or neutral zeolite catalyst. The catalyst can comprise one or morepromoters chosen from the group of alkali elements, alkaline earthelements, rare earth elements, Y, Zr, and Nb.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a flow chart for the production of styrene by thereaction of formaldehyde and toluene, wherein the formaldehyde is firstproduced in a separate reactor by either the dehydrogenation oroxidation of methanol and is then reacted with toluene to producestyrene.

FIG. 2 is a schematic illustration of an aspect of an embodiment of thepresent invention having the capability for continuous reaction withcatalyst regeneration.

DETAILED DESCRIPTION

Toluene has been used to produce styrene by reactions with eithermethanol or methane/oxygen as the co-feed. Theoretically methanol(CH₃OH) and toluene (C₆H₅CH₃) can be reacted together to form styrene,water and hydrogen gas, as shown below:CH₃OH+C₆H₅CH₃→C₈+H₂O+H₂

In practice, however, the methanol (CH₃OH) often dehydrogenates intoformaldehyde (CH₂O) and hydrogen gas (H₂). Often the toluene conversionis low or the selectivity to products of the methanol is too low to makethe process economical. Conversion of methanol to COx or methane canresult in an undesirable by-product stream that is not easily recovered.In order to avoid this undesirable side reaction, a method of producingstyrene utilizing a separate reactor to convert methanol intoformaldehyde is disclosed. Toluene can then be reacted directly withformaldehyde to produce styrene and water. This process avoids theinstability aspects of the methanol.

Formaldehyde can be produced either by the oxidation or dehydrogenationof methanol. Silver-based catalysts are most commonly used for thisprocess but copper can also be used. Iron-molybdenum-oxide catalysts aretypically used for the dehydrogenation route. A separate process for thedehydrogenation or oxidation of methanol into formaldehyde gas could beutilized.

A separation unit may then be used if needed in order to separate theformaldehyde from the hydrogen gas or water from the formaldehyde andunreacted methanol prior to reacting it with toluene for the productionof styrene. This separation would inhibit the hydrogenation of theformaldehyde back to methanol. Purified formaldehyde could then be sentto the second reactor and the unreacted methanol could be recycled. Theuse of formaldehyde for the side chain alkylation of toluene is shownbelow:CH₂O+C₆H₅CH₃→C₈H₈+H₂O

Formaldehyde can be produced by the oxidation of methanol to produceformaldehyde and water. The oxidation of methanol is described in theequation below:2CH₃OH+O₂→2CH₂O+2H₂O

Alternately formaldehyde can be produced by the dehydrogenation ofmethanol to produce formaldehyde and hydrogen gas. This method producesa dry formaldehyde stream that may be preferred as it would not requirethe separation of the water prior to the reaction of the formaldehydewith toluene. The dehydrogenation process is described in the equationbelow:CH₃OH→CH₂O+H₂

In order to prevent the hydrogenation of formaldehyde back to methanol,it is desirable to have the separation of formaldehyde from either wateror hydrogen gas prior to its reaction with toluene. Separating theformaldehyde from the other byproducts of the oxidation ordehydrogenation reaction would result in a stable formaldehyde streamthat could be used in the production of styrene.

Although the reaction has a 1:1 molar ratio of toluene and formaldehyde,the ratio of the feedstreams is not limited within the present inventionand can vary depending on operating conditions and the efficiency of thereaction system. If excess toluene or formaldehyde is fed to thereaction zone, the unreacted portion can be subsequently separated andrecycled back into the process. In one embodiment the ratio oftoluene:formaldehyde can range from between 100:1 to 1:100. In alternateembodiments the ratio of toluene:formaldehyde can range between from50:1 to 1:50; from 20:1 to 1:20; from 10:1 to 1:10; from 5:1 to 1:5;from 2:1 to 1:2.

In FIG. 1 there is a simplified flow chart of one embodiment of thestyrene production process described above. The first reactor (2) iseither a dehydrogenation reactor or an oxidation reactor. This reactoris designed to convert the first methanol feed (1) into formaldehyde.The gas product (3) of the reactor is then sent to a gas separation unit(4) where the formaldehyde is separated from any unreacted methanol andunwanted byproducts. Any unreacted methanol (6) can then be recycledback into the first reactor (2). The byproducts (5) are separated fromthe clean formaldehyde (7).

In one embodiment the first reactor (2) is a dehydrogenation reactorthat produces formaldehyde and hydrogen and the separation unit (4) is amembrane capable of removing hydrogen from the product stream (3).

In an alternate embodiment the first reactor (2) is an oxidative reactorthat produces product stream (3) comprising formaldehyde and water. Theproduct stream (3) comprising formaldehyde and water can then be sent tothe second reactor (9) without a separation unit (4).

The formaldehyde feed stream (7) is then reacted with a feed stream oftoluene (8) in the second reactor (9). The toluene and formaldehydereact to produce styrene. The product (10) of the second reactor (9) maythen be sent to an optional separation unit (11) where any unwantedbyproducts (15) such as water can separated from the styrene, unreactedformaldehyde and unreacted toluene. Any unreacted formaldehyde (12) andthe unreacted toluene (13) can be recycled back into the reactor (9). Astyrene product stream (14) can be removed from the separation unit (11)and subjected to further treatment or processing if required.

The operating conditions of the reactors and separators will be systemspecific and can vary depending on the feedstream composition and thecomposition of the product streams. The reactor (9) for the reaction oftoluene and formaldehyde will operate at elevated temperatures andpressures, such as for a non-limiting example from 250° C. to 750° C.and from 1 atm to 70 atm in pressure and may contain a basic or neutralcatalyst system.

Suitable catalysts for the reaction of toluene and formaldehyde caninclude as non-limiting examples metal oxides such as: CuO; ZnO—CuO;ZnO—CuO—Al₂O₃; CuCr₂O3; ZnCr₂O₃; or ZnO—CuO—Cr₂O₃. Other catalysts thatcan be used include metals supported on a substrate such as silica ortitania, for example: Ru; Rh; Ni; Co; Pd; or Pt. These can also containpromoters such as Mn, Ti, Zr, V, Nb, K, Cs, or Na. Still another groupof catalysts that can be used for the present invention include sulfidebased catalysts such as: MoS₂; WS₂; Mo₂WS₂; CoMoS₂; or NoMoS₂. Thesesulfide catalysts can include promoters such as K, Rb, Cs, Ca, Sr, Ba,La, or Ce.

The above catalysts can have toluene promoters added such as the alkali,alkaline earth, and/or rare earth elements. Other toluene promoters thatcan be added include Y, Zr, and/or Nb.

Improvement in side chain alkylation selectivity may be achieved bytreating a molecular sieve zeolite catalyst with proper chemicalcompounds to inhibit the external acidic sites and minimize aromaticalkylation on the ring positions. Another means of improvement of sidechain alkylation selectivity can be to impose restrictions on thecatalyst structure to facilitate side chain alkylation. In oneembodiment the catalyst used in an embodiment of the present inventionis a basic or neutral catalyst.

The catalytic reaction systems suitable for this invention can includeone or more of the zeolite or amorphous materials modified for sidechain alkylation selectivity. A non-limiting example can be a zeolitepromoted with one or more of the following: Ru, Rh, Ni, Co, Pd, Pt, Mn,Ti, Zr, V, Nb, K, Cs, or Na.

Zeolite materials suitable for this invention may include silicate-basedzeolites and amorphous compounds such as faujasites, mordenites,pentasils, etc. Silicate-based zeolites are made of alternating SiO₂ andMO_(x) tetrahedra, where M is an element selected from the Groups 1through 16 of the Periodic Table (new IUPAC). These types of zeoliteshave 8-, 10-, or 12-membered oxygen ring channels. An example ofzeolites of this invention can include 10- and 12-membered ringzeolites, such as ZSM-5, ZSM-11, ZSM-22, ZSM-48, ZSM-57, etc.

Embodiments of reactors that can be used with the present invention caninclude, by non-limiting examples: fixed bed reactors; fluid bedreactors; and entrained bed reactors. Reactors capable of the elevatedtemperature and pressure as described herein, and capable of enablingcontact of the reactants with the catalyst, can be considered within thescope of the present invention. Embodiments of the particular reactorsystem may be determined based on the particular design conditions andthroughput, as by one of ordinary skill in the art, and are not meant tobe limiting on the scope of the present invention. An example of a fluidbed reactor having catalyst regeneration capabilities that may beemployed with the present invention is illustrated in FIG. 2. This typeof reactor system employing a riser can be modified as needed, forexample by insulating or heating the riser if thermal input is needed,or by jacketing the riser with cooling water if thermal dissipation isrequired. These designs can also be used to replace catalyst while theprocess is in operation, by withdrawing catalyst from the regenerationvessel from an exit line (not shown) or adding new catalyst into thesystem while in operation.

FIG. 2 is a schematic illustration of an aspect of an embodiment of thepresent invention having the capability for continuous reaction withcatalyst regeneration. The reaction process (20) generally comprises twomain zones for reaction (21) and regeneration (22). A reaction zone canbe comprised of a vertical conduit, or riser (23), as the main reactionsite, with the effluent of the conduit emptying into a large volumeprocess vessel, which may be referred to as a separation vessel (24). Inthe reaction riser (23), a feed stream (25), such as toluene andformaldehyde, is contacted with a fluidized catalyst, which can be arelatively large fluidized bed of catalyst, at reactor conditions. Theresidence time of catalyst and hydrocarbons in the riser (23) needed forsubstantial completion of the reaction may vary as needed for thespecific reactor design and throughput design. The flowingvapor/catalyst stream leaving the riser (23) may pass from the riser toa solids-vapor separation device, such as a cyclone (26), normallylocated within and at the top of the separation vessel (24). Theproducts of the reaction can be separated from the portion of catalystthat is carried by the vapor stream by means of one or more cyclone (26)and the products can exit the cyclone (26) and separation vessel (24)via line (27). The spent catalyst falls downward to a stripper (28)located in a lower part of the separation vessel (24). Catalyst can betransferred to a regeneration vessel (22) by way of a conduit (29)connected to the stripper (28).

The catalyst can be continuously circulated from the reaction zone (21)to the regeneration vessel (22) and then again to the reaction zone(21). The catalyst can therefore act as a vehicle for the transfer ofheat from zone to zone as well as providing the necessary catalyticactivity. Catalyst from the reaction zone (21) that is being transferredto the regeneration zone (22) can be referred to as “spent catalyst”.The term “spent catalyst” is not intended to be indicative of a totallack of catalytic activity by the catalyst particles. Catalyst, which isbeing withdrawn from the regeneration vessel (22), is referred to as“regenerated” catalyst. The catalyst can be regenerated in theregeneration vessel (22) by heat and contact with a regeneration stream(30). The regeneration stream (30) can comprise oxygen and can comprisesteam. The regenerated catalyst can be separated from the regenerationstream by the use of one or more cyclones (31) that can enable theremoval of the regeneration vessel (22) via line (32). The regeneratedcatalyst can be transferred via line (33) to the lower section of theriser (23) where it is again in contact with the feed stream (25) andcan flow up the riser (23).

Use of broader terms such as comprises, includes, having, etc. should beunderstood to provide support for narrower terms such as consisting of,consisting essentially of, comprised substantially of, etc.

The term “molecular sieve” refers to a material having a fixed,open-network structure, usually crystalline, that may be used toseparate hydrocarbons or other mixtures by selective occlusion of one ormore of the constituents, or may be used as a catalyst in a catalyticconversion process.

Use of the term “optionally” with respect to any element of a claim isintended to mean that the subject element is required, or alternatively,is not required. Both alternatives are intended to be within the scopeof the claim. Use of broader terms such as comprises, includes, having,etc. should be understood to provide support for narrower terms such asconsisting of, consisting essentially of, comprised substantially of,etc.

The term “regenerated catalyst” refers to a catalyst that has regainedenough activity to be efficient in a specified process. Such efficiencyis determined by individual process parameters.

The term “spent catalyst” refers to a catalyst that has lost enoughcatalyst activity to no longer be efficient in a specified process. Suchefficiency is determined by individual process parameters.

The term “zeolite” refers to a molecular sieve containing a silicatelattice, usually in association with some aluminum, boron, gallium,iron, and/or titanium, for example. In the following discussion andthroughout this disclosure, the terms molecular sieve and zeolite willbe used more or less interchangeably. One skilled in the art willrecognize that the teachings relating to zeolites are also applicable tothe more general class of materials called molecular sieves.

Depending on the context, all references herein to the “invention” mayin some cases refer to certain specific embodiments only. In other casesit may refer to subject matter recited in one or more, but notnecessarily all, of the claims. While the foregoing is directed toembodiments, versions and examples of the present invention, which areincluded to enable a person of ordinary skill in the art to make and usethe inventions when the information in this patent is combined withavailable information and technology, the inventions are not limited toonly these particular embodiments, versions and examples. Other andfurther embodiments, versions and examples of the invention may bedevised without departing from the basic scope thereof and the scopethereof is determined by the claims that follow.

What is claimed is:
 1. A process for making styrene comprising: reactingtoluene and formaldehyde in one or more reactors over a metal oxideselected from a group consisting of CuO, ZnO—CuO, ZnO—CuO—Al₂O₃,CuCr₂O₃, ZnCr₂O₃, and ZnO—CuO—Cr₂O₃, to form a product stream comprisingstyrene.
 2. A process for making styrene comprising: converting methanolto formaldehyde in one or more first reactors to form a first productstream comprising formaldehyde; passing the first product stream to aseparation stage for separating formaldehyde from the first productstream; and reacting toluene and formaldehyde in one or more secondreactors over a metal oxide selected from a group consisting of CuO,ZnO—CuO, ZnO—CuO—Al₂O₃, CuCr₂O₃, ZnCr₂O₃, and ZnO—CuO—Cr₂O₃, to form asecond product stream comprising styrene.
 3. The process of claim 2,wherein the metal oxide includes one or more promoters selected fromalkali elements, alkaline earth elements, and rare earth elements. 4.The process of claim 2, wherein the metal oxide includes one or morepromoters selected from a group consisting of Y, Zr, Nb, andcombinations thereof.
 5. The process of claim 2, wherein the metal oxideis basic or neutral.
 6. The process of claim 2, wherein the toluene isreacted with the formaldehyde at a temperature ranging from 250° C. to750° C.
 7. The process of claim 2, wherein the toluene is reacted withthe formaldehyde at a pressure ranging from 1 atm to 70 atm.
 8. Theprocess of claim 2, wherein the first product stream further comprisesone or more of hydrogen, water, or methanol.
 9. The process of claim 2,wherein methanol is separated from the first product stream and recycledto the one or more first reactors.
 10. The process of claim 2, furthercomprising utilizing one or more oxidation reactors to convert methanolinto formaldehyde and water to form the first product stream.
 11. Theprocess of claim 2, further comprising utilizing one or moredehydrogenation reactors to convert methanol into formaldehyde andhydrogen to form the first product stream.
 12. The process of claim 2,wherein the second product stream further comprises one or more oftoluene, water, or formaldehyde.
 13. The process of claim 2, furthercomprising passing the second product stream to a second separationstage for separating styrene from the second product stream.
 14. Theprocess of claim 13, wherein toluene is separated from the secondproduct stream and recycled to the one or more second reactors.
 15. Theprocess of claim 13, wherein formaldehyde is separated from the secondproduct stream and recycled to the one or more second reactors.
 16. Theprocess of claim 2, wherein the first separation stage comprises amembrane to remove hydrogen from the first product stream.